E. L. Larson et al disclosed an inflation valve and gauge in their U.S. Pat. No. 1,582,523 to combine an inflation valve and a gauge on a wheel tire for measuring tire pressure directly on the tire. However, such a conventional gauge still has the following drawbacks:
1. In measuring operation, the slidable tube 12 and the secured graduated sleeve 19 are slidably movable on the main tube 2 secured on the tire. After a long time service, the washer or nut 20 or any other packing rings may be worn to cause air leakage therefrom to influence measuring precision or decreasing tire pressure to even cause an accident.
2. The expansible rubber tube 7 is not a closed bag or sac filled with air therein and is positioned proximate a tire outer layer so that the pressure value measured by this device is influenced by a temperature change outside a tire especially after a high-speed running of a wheel tire to exert a frictional heat increasing the tire temperature suddenly.
3. The valve and gauge is vertically extended for a distance from the tire 1, which will be subjected to centrifugal force during a rotation of wheels when running a car, to thereby easily deform or break the inflation valve and gauge.
The present inventor has found the drawbacks of the conventional tire gauge and invented the present tire gauge for an isothermal measurement of tire pressure.